Method for producing immobilized enzyme

ABSTRACT

A method for producing an immobilized enzyme which includes the steps of immobilizing an enzyme used for hydrolyzing fats and oils on a immobilization carrier by adsorption, bringing the immobilized enzyme into contact with an organic solvent in which fat-soluble fatty acids or the derivatives thereof have been dissolved, and adjusting the moisture content of the immobilized enzyme from 1 to 20% by weight based on the weight of the carrier.

FIELD OF THE INVENTION

The present invention relates to a method for producing immobilizedenzyme to be used as a catalyst of hydrolysis reaction of fats and oils(mono-, di-, or triglyceride), esterification reaction of fatty acidwith an alcohol, or transesterification reaction of fats and oils.

BACKGROUND OF THE INVENTION

The use of an enzyme for hydrolyzing fats and oils has been increased inmany cases of the production of hydrolysates of fats and oils (mono-,di-, or triglyceride), or the production of esters from fatty acids andalcohols by the reverse reaction of hydrolysis, and the production ofnew glycerides by exchanging acyl group of the fats and oils. Especiallyin the case of producing fats and oils with functionality, a lipasehaving a position specificity has been used frequently. And, in order torecover and reuse the lipase enzyme, an immobilized enzyme can be used.

Many of the immobilized enzymes which are available at present areoffered in a dried form, taking into consideration the inhibition of anenzyme from deactivation during storage and proper handling. However,deactivation of an immobilized enzyme is liable to occur at a step wherethe immobilized enzyme is dried under reduced pressure, in a vacuum orby heating, and the maximum activity of the immobilized enzyme is notachieved in many cases. Meanwhile, a method of water removal by treatingthe enzyme with organic solvent has been known (JP-A-2000-253874), butall the same, the maximum activity of the enzyme is not achieved againstthe original activity of the adsorbed enzyme.

On the other hand, a method for increasing the recovery of enzymeactivity has been proposed, wherein the drying of the immobilized enzymeis carried out by contacting with fatty acid derivatives(JP-A-1987-134090) In addition, a method for producing an immobilizedenzyme for esterification reaction showing high activity has beenpublished (JP-A-2000-166552, JP-A-2004-81200), wherein the deactivationof the enzyme is prevented by controlling the moisture content of theimmobilized enzyme by bringing the immobilized enzyme into contact witha fatty acid glyceride, or dehydrating after bringing the immobilizedenzyme into contact with the above glyceride.

SUMMARY OF THE INVENTION

The present invention provides a method for producing an immobilizedenzyme which includes the steps of immobilizing an enzyme used forhydrolyzing fats and oils on a immobilization carrier by adsorption,bringing the immobilized enzyme into contact with an organic solvent inwhich fat-soluble fatty acids or the derivatives thereof have beendissolved, and adjusting the moisture content of the immobilized enzymefrom 1 to 20% by weight based on the weight of the carrier.

DETAILED DESCRIPTION OF THE INVENTION

The above described method for drying the immobilized enzyme bycontacting with fatty acid derivatives is inefficient because theprocedure has to be carried out slowly, and also impractical because theestablishment of the drying condition or the like are complicated andexpensive equipments are needed. Also, the immobilized enzyme preparedby method of conducting dehydration of the enzyme under contacting withthe glycerides or the like after the above described enzyme isimmobilized by adsorption to the immobilization carrier, has a problemwith respect to its inconvenient form for handling because the enzyme isinfiltrated by glycerides of the fatty acid or the like.

The present inventors have found that, after the enzyme is immobilizedby adsorption to an immobilization carrier, the moisture content ofimmobilized enzyme can be controlled with maintaining high level ofenzyme activity, by contacting the immobilized enzyme with an organicsolvent in which fat-soluble fatty acids or the derivatives thereof havebeen dissolved, and also, the difficulty of handling can be improved atthe same time because the glycerides of fatty acids and the like cansufficiently be decreased in the immobilized enzyme.

The immobilization carrier for the immobilized enzyme to be used in thepresent invention includes inorganic carriers such as celite,diatomaceous earth, kaolinite, silica gel, molecular sieves, porousglass, activated carbon, calcium carbonate and ceramics, and organicpolymers such as ceramics powder, polyvinyl alcohol, polypropylene,chitosan, ion-exchange resins, hydrophobic adsorption resins, chelatingresins and synthetic adsorptive resins, and ion-exchange resins arepreferable.

As to the ion-exchange resins, porous anion-exchange resins arepreferable. such a porous carrier has a large surface area, whereby theadsorption of a large amount of enzyme may be attained. The particlesize of the resin is preferably from 100 to 1000 μm in diameter, and itspore size is preferably from 10 to 150 nm. The material for theimmobilization carrier includes phenol-formaldehyde, polystyrene, acrylamide, divinylbenzene and the like, and among them, the phenolformaldehyde resin (for example, Duolite A-568, produced by Rohm andHaas Co.) is more preferable.

As to the enzyme for hydrolyzing fats and oils to be used in the presentinvention, a lipase is preferable. The commercially available lipasesderived from microorganisms as well as those derived from animals orplants may be used. The lipase derived from microorganisms includes theenzymes produced by the microorganisms belonging to for example thegenus of Rizopus, Aspergillus, Mucor, Pseudomonas, Geotrichum,Penicillium, and Candida. Especially when the functional fats and oilsare aimed to be produced, use of a lipase having a position specificitywhich has ability to generate a binding selectively on the desiredposition of the glycerol, such as 1, 3-position-selective lipase derivedfrom the microorganisms belonging to the genus of Rizopus, Aspergillus,Mucor, Pseudomonas, Geotrichum, or Penicillium, is more preferable.

In immobilization of the enzyme, the enzyme maybe adsorbed directly onthe carrier, or, the carrier may be treated in advance with thefat-soluble fatty acids or the derivatives thereof before adsorbingthereon the enzymes in order to obtain such adsorption state that a highactivity is revealed. The fat-soluble fatty acid to be used in thepresent invention includes saturated or unsaturated fatty acids with 8to 18 carbon atoms with linear or branched chain, or the fatty acidshaving displaced hydroxyl group. Such fatty acids include, for example,capric acid, lauric acid, myristic acid, oleic acid, linoleic acid,α-linolenic acid, recinoleic acid, and isostearic acid. In addition, thederivatives of the fatty acids include the esters of the above fattyacids with monohydric or polyhydric alcohol, phospholipids, and theaddition derivatives of these esters with ethylene oxide. The fatty acidderivatives include, for example methyl ester, ethyl ester,monoglyceride, diglyceride, their addition compounds with ethyleneoxide, polyglycerol ester, sorbitan ester, and sucrose ester of theabove described fatty acids. Two or more of these fat-soluble fattyacids or the derivatives thereof may be used in combination.

The contact of these fat-soluble fatty acids or the derivatives thereofwith the carrier may be performed by adding these materials directly inwater or organic solvent, however, to attain a good dispersibility thefat-soluble fatty acids or the derivatives thereof may be dispersed anddissolved in an organic solvent beforehand and then added to the carrierdispersed in water. Such organic solvent includes chloroform, hexane,ethanol and the like. The amount of the fat-soluble fatty acids or thederivative thereof to be used is preferably from 1 to 500% by weight,and more preferably from 10 to 200% by weight based on the weight of thecarrier. The contact temperature is preferably from 0 to 100° C., andmore preferably from 20 to 60° C. The contact time is preferably fromabout 5 minutes to about 5 hours. The carrier processed by the abovedescribed treatment is recovered by filtration, and may be dried. Thedrying temperature is preferably from room temperature to 100° C., andmay be dried under reduced pressure.

The temperature of immobilization reaction can be determined based onthe characteristics of the enzyme, however, the temperature from 0 to60° C., at which deactivation of the enzyme does not occur, ispreferable and the temperature from 5 to 40° C. is more preferable. ThepH of the enzyme solution to be used for immobilization process may bewithin the range at which deactivation of the enzyme does not occur andit may be determined based on the characteristics of the enzyme as well;however, pH from 3 to 9 is preferable. To maintain this pH, a buffersolution is used, which includes acetate buffer solution, phosphatebuffer solution, and Tris-HCl buffer solution.

The concentration of the enzyme in the above described solution isdesirably lower than the saturation solubility while sufficientconcentration from the view point of maintaining immobilizationefficiency. Further, if needed, a supernatant solution after insolublesubstance in the enzyme solution is removed by centrifugal separation,or the solution purified by ultra filtration or the like may also beused as an enzyme solution. The amount of the enzyme to be used ispreferably from 5 to 1000% by weight , and more preferably from 10 to500% by weight based on the weight of the carrier.

After immobilization of the enzyme, the moisture content in theimmobilized enzyme is controlled by means of contacting the enzyme withan organic solvent in which fat-soluble fatty acids or the derivativesthereof have been dissolved. The remaining moisture content iscontrolled to be from 1 to 20% by weight based on the weight of thecarrier, and that from 2 to 15% by weight is preferable, and that from 3to 10% by weight is more preferable.

The preferable fat-soluble fatty acids to be used for the abovedescribed treatment are those derived from vegetal liquid fat such asrapeseed oil, soybean oil and sunflower oil, or fish oil such as sardineoil, tuna oil and bonito oil, and the derivatives thereof include thesefats and oils themselves and lower alcohol esters derived from thesefats and oils. Two or more kinds of these fatty acids may be used incombination. In addition, regarding the fat-soluble fatty acids or thederivatives thereof to be used in this process, it is preferable toselect from oil phase substrates, its hydrolysates, or its low alcoholesters in the actual hydrolysis reaction, esterification reaction, ortransesterification reaction catalyzed by the immobilized enzymeprepared according to the present invention.

The amount of fat-soluble fatty acids and the derivatives thereof to beused in this process is preferably from 1 to 500% by weight, and morepreferably from 10 to 200% by weight based on the weight of the carrierfrom the view point of getting sufficient contact with the immobilizedenzyme and avoiding waste of excessive use.

The organic solvent to be used for the above described treatmentincludes acetone, ethanol, and a mixture thereof. Among these organicsolvent, from the view point of prevention of the deactivation of theenzyme and volatile characteristics, acetone or a mixture of acetone andother organic solvent is preferable.

The amount of organic solvent to be used is preferably from 100 to 3000%by weight, and more preferably from 200 to 2000% by weight based on theweight of carrier from the view point of getting sufficient contact withthe immobilized enzyme and avoiding waste of excessive use.

The contact of the immobilized enzyme with an organic solvent in whichfat-soluble fatty acids or the derivatives thereof have been dissolvedmay be performed by any type of method selected from soaking,dispersion, stirring, passing the solvent through a column packed withthe immobilized enzyme by pumping, and the like. The contact temperaturemay be the temperature at which the oil phase does not solidify duringthe contact, and which may be determined optionally according to theproperties of the fat-soluble fatty acid or the derivatives thereof andthe enzyme, in particular, the temperature from 0 to 40° C. ispreferable, and that from 5 to 30° C. is more preferable. The contacttime is preferably from 1 to 30 minutes, and that from3 to 10 minutes ismore preferable. If needed, a plural time of treatment may be conducted.

The moisture content of the immobilized enzyme at the time when theenzyme is immobilized by adsorption on the carrier is generally withinthe range from 120 to 300% by weight based on the weight of the carrier;however the present invention can adjust the moisture content of theimmobilized enzyme from 1 to 20% by weight based on the weight of thecarrier by contacting with an organic solvent in which fat-soluble fattyacids or the derivatives thereof have been dissolved. By the abovedescribed treatment, damages to the enzyme that occurred at the processof forced removal of moisture such as common drying treatment may beminimized, and thus the immobilized enzyme with high activity may beprepared.

After completion of the contact process, the immobilized enzyme isrecovered by filtration, as appropriate.

EXAMPLES Example 1

A 100 g of Duolite A-568 (Rohm and Haas Co.) which was used as a carrierwas stirred in 1 L of 0.1 N NaOH solution for one hour. Afterfiltration, it was washed with 1 L of distilled water, and pH wasequilibrated with 1 L of 500 mM acetate buffer solution (pH 6). Then,the pH equilibration was repeated twice, each for 2 hours, with 1 L of50 mM acetate buffer solution (pH 6). After recovery of the carrier byfiltration, solvent replacement was carried out using 500 mL of ethanolfor 30 minutes. After filtration, the carrier was contacted for 30minutes with 500 mL of ethanol solution containing 100 g of recinoleicacid. After filtration, solvent replacement by buffer solution wascarried out 4 times with each 500 mL of 50 mM acetate buffer solution(pH 6) for 30 minutes. After filtration, adsorption of the enzyme wasperformed by contacting the carrier with 1000 mL of 3% Lipase F-AP15(Amano Enzyme Inc.) solution for 2 hours at room temperature. Afteradsorption the enzyme-adsorbed carrier was recovered by filtration, andwashed with 500 mL of 50 mM acetate buffer solution (pH 6) for 30minutes. After washing, the immobilized enzyme was recovered byfiltration.

To this immobilized enzyme, a solution of 100 g of oleic acid dissolvedin 500 g of acetone was added, and stirred at 20° C. for 5 minutes, andthen the immobilized enzyme was recovered by filtration. At this time,the amount of remaining moisture in the immobilized enzyme was 7.9% byweight based on the weight of the carrier.

Example 2

The immobilized enzyme was prepared and recovered by the same procedureas described in Example 1. To this immobilized enzyme, a solution of 200g of oleic acid dissolved in 800 g of acetone was added, and stirred at20° C. for 5 minutes, and then the immobilized enzyme was recovered byfiltration. At this time, the amount of remaining moisture in theimmobilized enzyme was 6.5% by weight based on the weight of thecarrier.

Example 3

The immobilized enzyme was prepared and recovered by the same procedureas described in Example 1. To this immobilized enzyme, a solution of 100g of rapeseed oil dissolved in 500 g of acetone was added, and stirredat 20° C. for 5 minutes, and then the immobilized enzyme was recoveredby filtration. At this time, the amount of remaining moisture in theimmobilized enzyme was 7.7% by weight based on the weight of thecarrier.

Comparative Example 1

The immobilized enzyme was prepared and recovered by the same procedureas described in Example 1. To this immobilized enzyme, 500 g of acetonewas added, and stirred at 20° C. for 5 minutes, and then the immobilizedenzyme was recovered by filtration. At this time, the amount ofremaining moisture in the immobilized enzyme was 7.2% by weight based onthe weight of the carrier.

Comparative Example 2

The immobilized enzyme was prepared and recovered by the same procedureas described in Example 1. To this immobilized enzyme, 1000 g of oleicacid was added, and stirred at 40° C. for 2 hours, and then theimmobilized enzyme was recovered by filtration. At this time, the amountof remaining moisture in the immobilized enzyme was 134% by weight basedon the weight of the carrier.

Comparative Example 3

The immobilized enzyme was prepared and recovered by the same procedureas described in Example 1. To this immobilized enzyme, 1000 g ofrapeseed oil was added, and stirred at 40° C. for 2 hours, and then theimmobilized enzyme was recovered by filtration. At this time, the amountof remaining moisture in the immobilized enzyme was 30% by weight basedon the weight of the carrier.

Test Example 1

The measurement of the relative activity and the evaluation of theeasiness of handling of each immobilized enzyme were carried outaccording to the procedures described below.

[Measurement of the Relative Enzyme Activity]

4 g of the immobilized enzyme as dry weight was weighed, and put into a200 mL four-neck flask. 80 g of a mixture of oleic acid and glycerol(oleic acid/glycerol=2.0 by molar ratio) was added into the flask tocarry out the esterification reaction under reduced pressure of 400 Paat 50° C. The reaction mixture was sampled occasionally and the changeof the glyceride composition over time was followed up. In addition, theglyceride composition of each sample of reaction mixture was analyzed bygas chromatography after the sample was trimethylsilylated. The activityof the immobilized enzyme was defined as the time taken for coming upthe sum of diglyceride (DG) plus triglyceride (TG) to 70% by weight, andrepresented by a relative value to the activity of Example 1 which wasassumed as 100%. The results were shown in Table 1.

[Evaluation of the Easiness of Handling of the Immobilized Enzyme)

The easiness of handling of the immobilized enzyme was evaluated by thepassage rate through a sieve.

The sieving test was carried out using about 100 g of the immobilizedenzyme as dry weight. Using a standard sieve of 200 mm diameter with 1.7mm sieve pore, the immobilized enzyme loaded on the sieve was shaken for30 minutes, and the passage rate was calculated by measuring the weightof immobilized enzyme appeared under the sieve. The results were shownin Table 1.

When the passage rate is 100% by weight, aggregation of the immobilizedenzyme is not observed, and the immobilized enzyme passes through thesieve smoothly. In such case, homogeneous packing of the immobilizedenzyme into an enzyme column can be performed easily resulting the speedup of work, and consequently, the significant increase of laborefficiency may be attained by the reduction of working time. TABLE 1Example Example Example C.E.^(†) C.E.^(†) C.E.^(†) 1 2 3 1 2 3 Oleicacid (wt % based on the weight of the carrier) 100 200 — — 1000 —Rapeseed oil(wt % based on the weight of the carrier) — — 100 — — 1000Acetone(wt % based on the weight of the carrier) 500 800 500 500 — —Treatment temperature (° C.) 20 20 20 20 40 40 Treatment time (minutes)5 5 5 5 120 120 Moisture content of the immobilized enzyme aftertreatment (wt % 7.9 6.5 7.7 7.2 134 30 based on the weight of thecarrier) Sieve passage rate of the immobilized enzyme (% by weight) 100100 100 100 7 16 Relative activity (%) 100 102 95 70 95 200^(†)C.E.: Comparative Example

From the results shown in Table 1, the immobilized enzyme which has beentreated only by fats and oils after immobilization (Comparative Example3: C.E. 3) have maintained sufficient enzyme activity, but the moisturecontent of the immobilized enzyme was not small, and had the drawback inhandling. Also, the immobilized enzyme which has been treated only byfatty acid after immobilization (Comparative Example 2: C.E. 2) was notreduced moisture content in the immobilized enzyme and quite difficultin handling, and the enzyme activity was slightly decreased. Further,the immobilized enzyme which has been treated only by organic solvent(Comparative Example 1: C.E. 1) was easy for handling but observedsignificant decrease in activity. In consequence, it is expected fromthe results of Comparative Examples of 1 through 3 that when thetreatment with organic solvent and fatty acid is carried out at the sametime, the activity decreases and handling is not improved so much.

However, the immobilized enzyme prepared according to the method of thepresent invention, which was contacted after immobilization with anorganic solvent in which fat-soluble fatty acids or the derivativesthereof have been dissolved, had the same easiness for handling as thattreated with organic solvent only, and maintained enzyme activity inhigh level. These results were far beyond expectation of the presentinventors.

1. A method for producing an immobilized enzyme which comprises thesteps of immobilizing an enzyme used for hydrolyzing fats and oils on aimmobilization carrier by adsorption, bringing the immobilized enzymeinto contact with an organic solvent in which fat-soluble fatty acids orthe derivatives thereof have been dissolved, and adjusting the moisturecontent of the immobilized enzyme from 1 to 20% by weight based on theweight of the carrier.
 2. The method for producing an immobilized enzymeaccording to claim 1, wherein the amount of fat-soluble fatty acid orthe derivatives thereof to be dissolved in an organic solvent is from 1to 500% by weight based on the weight of the carrier.
 3. The method forproducing an immobilized enzyme according to claim 1, wherein thefat-soluble fatty acids or the derivatives thereof to be dissolved in anorganic solvent are an oil phase substrate of the enzyme.
 4. The methodfor producing an immobilized enzyme according to claim 1, wherein theorganic solvent is acetone.